We would like to have a detailed picture of the processing, functions and assembly of the proteins of human respiratory syncytial virus (RSV). In previous years, we determined the primary structures of the viral proteins from sequencing cloned viral genes. This also identified various protein domains that were either tolerant or intolerant of amino acid substitutions, and also provided other clues to protein function. The folding, processing, and oligomerization of the F and G transmembrane glycoproteins were studied in detail using biochemical and cDNA mutation/expression techniques. This is now being extended to the third transmembrane glycoprotein, the SH protein. Also, we recently developed an experimental system in which in vitro-synthesized, truncated analogs of viral genomic RNA are transfected into tissue culture cells and rendered biologically active by complementation with viral proteins supplied by RSV superinfection. We are now working to achieve complementation using cDNA- expressed viral proteins in place of RSV. This would allow us to identify the viral proteins required for transcription, replication and virus production and would subsequently allow us to perform detailed structure- function studies of individual proteins.